The invention relates generally to the field of manually-operated push-pull controls. More specifically, the invention relates to the field of push-pull controls that operate with both linear and rotational inputs. Push-pull controls are used in various applications, such as throttle controls and controls for fuel mixtures.
One common prior art push-pull control 100, partially shown in FIG. 1, operates solely using linear input. In the prior art push-pull control 100, a panel nut 101 is fastened to a stationary element (e.g., an instrument panel, a housing, et cetera). A push rod 102 extends through the panel nut 101 and is movable relative to the panel nut 101, and a user input knob 103 is coupled to a proximal end 102a of the push rod 102 (e.g., by nut 104). A distal end (not shown) of the push rod 102 may be coupled to the apparatus being controlled, either directly or (more commonly) through a cable or other force-transferring device. If a cable is used, swiveling apparatus may couple the cable to the push rod 102, such that the cable is not crimped by rotation of the push rod 102.
To allow the push rod 102 to temporarily remain in a desired location relative to the panel nut 101, packing 105 (e.g., leather washers) surrounds the push rod 102, and a friction nut 106 is used to selectively compress the packing 105. Threading on the friction nut 106 is generally received by threading (not shown) in the panel nut 101. The geometry of the friction nut 106 and panel 101 includes internal cones so that the packing 105 is compressed radially inward to increase the friction on the push rod 102. Loosening the friction nut 106 relative to the panel nut 101 allows the packing 105 to relax. When the packing 105 is compressed, friction is formed between the packing 105 and the push rod 102; this friction may allow the push rod 102 to temporarily remain in a desired location relative to the panel nut 101. It should be appreciated that the amount of friction may be modified by adjusting how much the packing 105 is compressed. Even with maximum compression, however, it is generally possible to overcome this friction by pushing or pulling the push rod 102 (when gripping the user input knob 103). Rotating the push rod 102 (e.g., using the user input knob 103), on the other hand, generally has no effect, and various structure may optionally be used to restrict the push rod 102 from rotating relative to the panel nut 101. FIG. 1 shows the friction nut 106 entirely released from the panel nut 101 for illustration, but in use the friction nut 106 would generally be at least minimally coupled to the panel nut 101.
Another prior art push-pull control 200, referred to herein as a Standard Vernier Control, is shown in FIG. 2. A threaded tube 201 is threadably coupled to a panel nut 202, and a nut 203, and the elements 201, 202, 203 are fixed to a stationary element (e.g., an instrument panel, a housing, et cetera) by sandwiching the stationary element between the panel nut 202 and the nut 203. As shown, a lock washer 204 may also be included. The threaded tube 201 is generally hollow, and a helical surface 205 extends along the inside of the threaded tube 201. In the Standard Vernier Control 200, the helical surface 205 is formed by a spring 206.
A push rod 208 extends through the panel nut 202 and inside the threaded tube 201, and a user input knob 209 is coupled to a proximal end 208a of the push rod 208 (e.g., by a pair of nuts 210). A cable 212 is shown coupled to a distal end 208b of the push rod 208 by a pair of bearings 213 surrounding an end 212a of the cable 212 (or “cable terminal” 212a).
A release shaft 215 extends inside the push rod 208, and a release button 216 is coupled to a proximal end 215a of the release shaft 215. A spring 217 biases the button 216, and thus the release shaft 215, to an extended configuration (as shown). A distal end 215b of the release shaft 215 has a wedge-shaped configuration forming a cavity 218, and a ball 220 is positioned inside the cavity 218. When the button 216 and the release shaft 215 are at the extended configuration, the wedge-shaped configuration of the release shaft distal end 215b forces the ball 220 to interact with the helical surface 205 (formed by the spring 206); this interaction prohibits the push rod 208 from being pushed or pulled relative to the threaded tube 201 and the panel nut 202. The ball 220 may travel along the helical surface 205, however. As such, the user input knob 209 may be rotated, causing the push rod 208 to move inwardly/outwardly relative to the threaded tube 201 and the panel nut 202. Depending particularly on the amount of incline in the helical surface 205, inward/outward movement of the push rod 208 may be finely controlled by rotating the user input knob 209 in this manner.
It is not always desirable to rotate the user input knob 209, however, as (for example) it may be desirable to quickly move the push rod 208 a relatively large distance or to move the push rod 208 a relatively large distance without the effort of continuously rotating the user input knob 209. To operate the Standard Vernier Control 200 with linear—instead of rotational—input, the button 216 may be pressed to overcome the force of the spring 217. When the button 216 is pressed, the button 216 and the release shaft 215 are no longer at the extended configuration, and the ball 220 is released and allowed to separate from the helical surface 205. Without the ball 220 interacting with the helical surface 205, the push rod 208 may be pushed or pulled relative to the threaded tube 201 and the panel nut 202. However, rotational input may not be used to move the push rod 208 until the button 216 and the release shaft 215 return to the extended configuration.
While the Standard Vernier Control 200 has been generally well-received by the market, there are at least four disadvantages of the Standard Vernier Control 200. First, the distance that the control 200 can operate using rotational input is limited by the length of the helical surface 205, which can result in a threaded tube 201 that is unacceptably long for some applications. Second, the button 216 must be pressed to allow the push rod 208 to be moved using linear input. Third, if the button is not completely depressed, the linear motion is “ratchety” such that resistance is detected as the ball contacts each thread of the helical surface. Fourth, the ball 220 can “jam”, causing it to not automatically release when the button 216 is pressed and the release shaft 215 is no longer at the extended configuration. When this happens, there is a delay before linear input may be used to move the push rod 208. If the Standard Vernier Control 200 is being used to control an aircraft throttle, for example, such a delay could be life threatening or even deadly.